A more efficient way to prove message
origin is, as with data integrity, to use a digital signature. Remember
that a digital signature is a message digest encrypted with the senders
private key, which is used by a documents receiver to verify
that:

The message has not been tampered with since
it was signed (data integrity).

The person who supposedly sent the message really
did (this is non-repudiation).

A receiver may wish the verification
of a public key, to make sure that the public key they have really is
assigned to the person claiming to have sent the message. This is done
through the Public Key Infrastructure, using certificates, described
in the next major section.

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